An example of a window regulator apparatus is disclosed in Japanese Patent Laid-Open Publication No. 6-212857.
The window regulator apparatus includes a pair of pulleys, a drum and a cable. The pulleys are arranged at a distance from each other along the vertical direction of a vehicle door and rotatably supported to a door panel of the vehicle door, respectively. The drum is rotatably supported to the door panel and contains a spiral groove formed in an outer surface. A slant portion is formed in the outer surface of the drum so as to gradually increase its diameter. The cable is guided to the pulleys and is supported in the spiral groove so as to be looped around the drum. The cable is joined to a window glass through a carrier bracket which is fixed to the window glass.
When the drum rotates in the clockwise direction, a first extending portion of the cable which is extended from the drum to the upper pulley is wired to the drum and a second extending portion of the cable which is extended from the drum to the lower pulley is released from the drum. Therefore, a connecting point of the cable connected with the cable and the carrier bracket travels along the vertical direction of the vehicle door. As a result, the window glass moves along the vertical direction of the vehicle door from an opening position to close a vehicle window.
When the drum rotates in the counterclockwise direction, the first extending portion of the cable is released from the drum and the second extending portion of the cable is wired to the drum. Therefore, the connecting point of the cable travels along the vertical direction of the vehicle door. As a result, the window glass moves along the vertical direction of the vehicle door form a closing position to open the vehicle window opens.
Also, when the drum rotates, extending points of the cable relative to the drum are traveling on the slant portion of the drum by being supported in the spiral groove. Therefore, a moving speed of the window glass changes.
However, when the extending points are traveling on the slant portion, a wired quantity of the cable is different from a released quantity of the cable. The diameter of the drum which corresponds to the extending point of the first extending portion of the cable is different from the diameter of the drum which corresponds to the extending point of the second extending portion of the cable because of the slant portion of the drum. Therefore, the cable loosens relative to the spiral groove.